1. Field of the Invention
The present invention relates to a method for preventing staining by adhesion of organisms to marine structures, marine vessels, pipelines or channels for transferring sea water, fishing nets and fish preserve nets, or screens of sea water intake ports, which includes an apparatus for carrying out the method.
2. State of the Art
To portions which always contact with sea water such as pipe lines for transferring sea water as cooling water and screens of sea water intake ports in power plants, ship's piers, floating stations, bridge girders, marine organisms such as various seaweeds, barnacles and other shellfishes adhere, and the adhesion causes problems such as decrease in water intake amount, decrease in navigation speed of marine vessels. Therefore, adhered marine organisms must be removed at regular intervals, which is a difficult operation.
The mechanism of adhesion of marine organisms follows such an order that at first microorganisms such as a red tide microorganism adhere to allow a organism coating film to be formed, and larvas of large organisms such as barnacles adhere thereto. Therefore, to prevent adhesion of microorganisms and prevent adhesion and growth of large organisms is an effective solving measure for the above mentioned problems, and various procedures for which have been proposed.
The first one thereof is to make the surface which contacts with sea water to be smooth. It is difficult for the organisms to adhere to the smooth surface, but its effect is only at early stages, consequently resulting in suffering adhesion. Therefore, this not a long-lasting countermeasure.
Those procedures which are often used for preventing stains of ships are paints containing an organic tin compound. The organic tin compound elutes from a paint film of the stain preventing paint to sea water, and kills bacteria in the neighborhood, thereby adhesion of marine organisms can be prevented. The effect of the stain preventing paint generally continues only about two years, so that repainting is necessary at regular intervals, and the ship must be entered into a dry dock. This procedure cannot be applied to the fixed structures, and use of the stain preventing paint is also being restricted due to pollution of the environment.
As a stain preventing method for pipelines for transferring sea water, there is a method in which chlorine is injected into the pipes. Since chlorine is harmful, another problem takes place for handling it.
There is a method in which copper or a copper alloy is used as an electrode to arrange closely near to an article subjected to stain prevention to give an anode, and direct current is allowed to flow to generate copper ion (Japanese Patent Disclosures No. 61-136689, No. 61-221382, No. 61-221383, No. 61-221384 and No. 63-142109). Also, there is a method in which an insoluble electrode is used, and sea water is electrolized to generate chlorine ion (Japanese Patent Disclosures No. 63-101464, No. 63-103789, No. 64-87791 and No. 64-168224). In these methods, a bacteriocidal substance generated by electrochemical reaction covers surroundings of the article subjected to stain prevention, thereby stain prevention is performed. Thus, application of this method is difficult where sea water flows fast. In addition, it is not preferable to generate the substance which is harmful for living bodies.